In the state of the art, centering diaphragms for loudspeakers are generally built so that one edge of a disk-shaped sleeve, which is wavy when viewed from the side, is connected to the loudspeaker frame, and the other edge to the voice coil support or the loudspeaker diaphragm. Such sleeves are usually made of natural fibers or plastic, and are also impregnated, for example with synthetic resin. The connection of the sleeve edges to the usual components of the loudspeaker is mostly achieved with an adhesive.
Although such devices can be used up to about 100 degrees Celsius without any problems, considerable problems occur when such loudspeakers are used above the cited temperature range, since the adhesive bonds and/or the impregnations are then no longer stable.
A centering device for loudspeakers is known from document U.S. Ser. No. 08/163,662 (now abandoned), which claims priority from German patent DE 42 41 212, which also serves as the starting point for this patent application, and makes the use of sleeve-shaped centering diaphragms superfluous in addition to remaining stable at very high operating temperatures.
There, a rod is placed on the pole body of the magnet system and is centered with the loudspeaker axis. A bushing is placed over this rod, which surrounds the outer casing of the rod at a small distance, and can slide on the rod in the lengthwise direction of the loudspeaker axis. The outer casing of the bushing is connected to the voice coil support. A spiral spring is stretched between the lower edge of the bushing and the pole body, and also between the upper edge of the bushing and a dish connected to the upper end of the rod, which, in the idle position of the system, locates the voice coil connected to the voice coil support in the plane of the pole plate. The distance between the inner case of the bushing and the outer case of the "strands" must be small, in order to properly center the rod/bushing assembly. However, this proximity of both parts can lead to touching of the respective casing surfaces of bushing and rod during the excursions of the voice coil support. Such touching impedes the free excursion of the voice coil support and leads to distortion of the sound reproduced by the loudspeaker. In this connection it is especially disadvantageous when dirt particles accumulate in the gap between rod and bushing, since these particles also increase the friction between bushing and rod.
It is therefore the task of the invention to provide sleeveless centering for loudspeakers, which eliminates any touching of rod and bushing.